Debye relaxation mechanisms of microwave heating of near-critical polar gases

Abstract

In this work, the average time of slow dielectric relaxation in sub- and supercritical polar gases is considered in terms of a combination of two Debye relaxation mechanisms. Under the assumption of thermal equilibrium, the corresponding relaxation times are theoretically predicted to be proportional to the mean binary collision time and mean translational deceleration time of free molecules with the proportionality factor close to unity. The microwave heating rate for pressurized pure gases and gas mixtures in constant-pressure and constant-density conditions is found from the Poynting formula. Temperature-dependent frequency spectra of the isobaric and isochoric heating rates for sub- and supercritical water are obtained with an allowance for non-Debye high-frequency relaxations. Perceptible temperature effects in the supercritical water heating rates at relaxation frequency are predicted when pressures/densities are high enough and considerable reduction of the heating time for higher pressures/densities is expected.